1. Field of the Invention
The present invention relates to a speed sensorless vector control apparatus capable of controlling the vector of an AC motor such as an induction motor, etc. without a speed sensor.
2. Description of the Related Art
In vector control known as a high-performance and high-precision system of controlling an induction motor, speed information about a motor is required, and is normally obtained by a pulse generator (PG), etc. However, it is desired to realize the speed sensor vector control as a variable speed drive system capable of performing torque control and obtaining the maximum torque in a wide operation range without a necessity of the high performance of the conventional speed sensor vector control at a request to restrict the environment of setting a speed sensor, simplify the wiring, reduce the cost, etc.
FIG. 1 is a block diagram of the function of the conventional speed sensorless vector control apparatus using a common speed adaptive secondary flux observer, and shows the speed sensor vector control of an AC motor 102 such as an induction motor, etc. by combining an inverter 101, a current detection unit 103, current adjustment units 104 and 105, coordinate conversion units 106 and 109, 3 phase to 2 phase conversion units 107 and 108, a current/flux estimation unit 110, and a speed estimation unit 301.
The current/flux estimation unit 110, the speed estimation unit 301, etc. configure the speed adaptive secondary flux observer.
In FIG. 1, a primary current 118 of the AC motor 102 through the 3 phase to 2 phase conversion unit 108 is converted into a d-q axis rotation coordinate component by the coordinate conversion unit 109 with an estimated flux (vector) 122 set as the standard of a rotation coordinate, and then into a torque current (iq) 117 and a magnetization current (id) 116. The current adjustment units 104 and 105 perform control such that the torque current (iq) 117 and the magnetization current (id) 116 respectively match a torque current command (iq*) 113 and a magnetization current command (1d*) 115. The magnetization current command (1d*) 115 is computed by a magnetization current command operation unit 112 which receives a flux command ("PHgr"*) 114.
The coordinate conversion unit 106 generates a primary voltage command 119 by converting the output of the current adjustment units 104 and 105 into a static coordinate system, generating a primary voltage command 119, and providing the generated command for the inverter 101 such as a three-phase voltage type inverter, etc. The inverter 101 performs DC-AC conversion based on the primary voltage command 119, and provides the voltage (primary voltage 120) of each of the three phases for the AC motor 102.
In addition, the primary voltage 120 and a primary current 118 detected by the current detection unit 103 are converted into two components respectively by the 3 phase to 2 phase conversion units 107 and 108. The two-phase component of the primary voltage 120 is input to the current/flux estimation unit 110, the two-phase component of the primary current 118 is input to the current/flux estimation unit 110, the speed estimation unit 301, and the coordinate conversion unit 109.
Described mainly below are the operations by the current/flux estimation unit 110 and the speed estimation unit 301 to explain about the speed estimating operation in the conventional speed sensorless vector control.
First, the principle of the speed sensorless vector control is introduced by:
Document 1: Power and Electric Application Study of Electric Society of Japan, material IEA-91-11, 1991, pp. 41-48 xe2x80x9cSpeed Adaptive Secondary Flux Observer of an Induction Motor and its Characteristicsxe2x80x9d
Document 2: IEEE Transaction on Industry Application, Vol. 30, No. 5, September/October 1994, pp. 1219-1224 xe2x80x9cSpeed Sensorless Field Oriented Control of Induction Motor with Rotor Resistance Adaptationxe2x80x9d
Document 3: xe2x80x9cVector Control of AC Motorxe2x80x9d (published by Daily Industrial News in 1996, pp. 91-110, Chapter 5 xe2x80x98Speed Sensor Vector Control of Induction Motorxe2x80x99.
According to the above mentioned documents, the speed can be estimated based on the algorithm described below with the configuration shown in FIG. 2 described later.
First, in an example of an induction motor as a motor to be controlled, a state equation can normally be represented by equation 1. The transposed matrix is expressed with the character T added to a matrix as a superscript.                                           ⅆ                          /                              ⅆ                                  t                  ⁡                                      [                                                                                                                        i                            s                                                                                                                                                                            φ                            r                                                                                                                ]                                                                                =                                    A              ⁡                              [                                                                                                    i                        s                                                                                                                                                φ                        r                                                                                            ]                                      +                          Bv              s                                      ⁢                  
                ⁢                                            i              s                        =                                          [                                                                                                    i                                                  s                          ⁢                                                      xe2x80x83                                                    ⁢                          α                                                                                                                                    i                                                  s                          ⁢                                                      xe2x80x83                                                    ⁢                          β                                                                                                                    ]                            T                                ;                ⁢                  
                ⁢                                            φ              r                        =                                          [                                                                                                    φ                                                  r                          ⁢                                                      xe2x80x83                                                    ⁢                          α                                                                                                                                    φ                                                  r                          ⁢                                                      xe2x80x83                                                    ⁢                          β                                                                                                                    ]                            T                                ;                ⁢                  
                ⁢                                            v              s                        =                                          [                                                                                                    v                                                  s                          ⁢                                                      xe2x80x83                                                    ⁢                          α                                                                                                                                    v                                                  s                          ⁢                                                      xe2x80x83                                                    ⁢                          β                                                                                                                    ]                            T                                ;                ⁢                  
                ⁢                              A            =                          [                                                                                                                  -                                                  (                                                                                                                    R                                s                                                                                            σ                                ⁢                                                                  xe2x80x83                                                                ⁢                                                                  L                                  s                                                                                                                      +                                                                                          1                                -                                σ                                                                                            σ                                ⁢                                                                  xe2x80x83                                                                ⁢                                                                  τ                                  r                                                                                                                                              )                                                                    ⁢                      I                                                                                                                                                    L                          m                                                                          σ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      L                            s                                                    ⁢                                                      L                            r                                                                                              ⁢                                              (                                                                                                            1                                                              τ                                r                                                                                      ⁢                            I                                                    -                                                                                    ω                              r                                                        ⁢                            J                                                                          )                                                                                                                                                                                                          L                          m                                                                          τ                          r                                                                    ⁢                      I                                                                                                                                                    -                                                      1                                                          τ                              r                                                                                                      ⁢                        I                                            +                                                                        ω                          r                                                ⁢                        J                                                                                                        ]                                ;                ⁢                  
                ⁢                              B            =                                          [                                                                                                    1                                                  σ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      L                            s                                                                                                                                      0                                                              0                                                              0                                                                                                  0                                                                                      1                                                  σ                          ⁢                                                      xe2x80x83                                                    ⁢                                                      L                            s                                                                                                                                      0                                                              0                                                                      ]                            T                                ;                ⁢                  
                ⁢                              I            =                          [                                                                    1                                                        0                                                                                        0                                                        1                                                              ]                                ;                ⁢                  
                ⁢                              J            =                          [                                                                    0                                                                              -                      1                                                                                                            1                                                        0                                                              ]                                ;                                    Equation        ⁢                  xe2x80x83                ⁢        1            
In the equation 1 above,
is and vs indicate the primary current and the primary voltage;
xcfx86r indicates the secondary interlinkage flux (secondary flux);
Superscripts xcex1 and xcex2 indicate the orthogonal 2-axis component s of a static coordinate system;
Rs and Rr indicate the primary resistance and the secondary resistance;.
Ls, Lr, and Lm indicate the primary inductance, the secondary inductance, and the mutual inductance respectively;
xcfx84r=Lr/Rr indicates the secondary time constant;
"sgr"=1xe2x88x92Lm2/(LsLr) indicates a leakage coefficient; and
xcfx89r indicates a rotor angular speed.
The equation 1 indicates the relationship between the primary voltage vs as an input to a control target and the primary current is and the secondary flux xcfx86r as outputs. If the primary voltage vs is provided, the primary current is and the secondary flux xcfx86r can be computed.
A model in which the above mentioned deviation can be input to a simulator such that there is no deviation between an output of a control target which can be measured and an estimated output value of the simulator is referred to as a same dimensional observer. According to the principle of the observer, the current/flux estimation unit 110 computes the estimated value is{circumflex over ( )} of the primary current (an estimated current 121 shown in FIG. 1) and the estimated value xcfx86r{circumflex over ( )} of the secondary flux (an estimated flux 122) by equation 2. In the following descriptions, xe2x80x9c{circumflex over ( )}xe2x80x9d indicates an estimated value.                               ⅆ                      /                          ⅆ                              t                ⁡                                  [                                                                                                              i                          s                          ^                                                                                                                                                              φ                          r                          ^                                                                                                      ]                                                                    =                                            A              ^                        ⁡                          [                                                                                          i                      s                      ^                                                                                                                                  φ                      r                      ^                                                                                  ]                                +                      Bv            s                    +                      G            ⁡                          (                                                i                  s                  ^                                -                                  i                  s                                            )                                                          Equation        ⁢                  xe2x80x83                ⁢        2            
In the equation 2 above,
G indicates a gain matrix (optional matrix for determination of the dynamic characteristic of an observer).
A matrix A{circumflex over ( )} is obtained by replacing the angular speed xcfx89r in the matrix A in the equation 1 with the estimated speed xcfx89r{circumflex over ( )}.
In the equation 2 above, when the rotor angular speed changes, there arises deviation between the output (primary current estimated value) of the simulator (equation model) and the actual primary current. Thus, the speed adaptive secondary flux observer estimates the secondary flux xcfx86r while estimating and adapting the angular speed xcfx89r using the function of the current deviation (isxe2x88x92is{circumflex over ( )}).
The speed adaptive secondary flux observer can be configured as expressed by equation 3 described later by adding the adaptive estimation mechanism of the angular speed as an unknown parameter to the observer expressed by the equation 2, and can be embodied by the speed estimation unit 301 shown in FIG. 1 obtaining an estimated speed 123 from the estimated current 121, the primary current 118, and the estimated flux (vector) 122.
That is, as shown in FIG. 2 of an embodiment of the. speed estimation unit 301 shown in FIG. 1, an outer product unit 202 obtains an outer product of the current deviation (isxe2x88x92is{circumflex over ( )}) obtained by an addition/subtraction unit 203 and the estimated flux (xcfx86r{circumflex over ( )}) 122, and the speed estimation unit 301 provides the outer product to a PI adjustment unit 201, and obtains the estimated speed (xcfx89r{circumflex over ( )}) 123.
That is, the estimated speed xcfx89r{circumflex over ( )} is computed by the following equation 3. The symbol x in the equation 3 indicates an outer product.
xcfx89r{circumflex over ( )}=(kpxcfx89+kixcfx89/p){(isxe2x88x92is{circumflex over ( )})xc3x97xcfx86r{circumflex over ( )}}=(kpxcfx89+kixcfx89/p){(isxcex1xe2x88x92isxcex1{circumflex over ( )})xcfx86rxcex2{circumflex over ( )}xe2x88x92(isxcex2xe2x88x92isxcex2{circumflex over ( )})xcfx86rxcex1{circumflex over ( )}}xe2x80x83xe2x80x83Equation 3
p=d/dt
In the equation 3 above,
kpxcfx89 and kixcfx89 indicate a proportional gain and an integral gain respectively;
isxcex1, isxcex1{circumflex over ( )}, isxcex2, and isxcex2{circumflex over ( )} indicate the orthogonal 2-axis component in the static coordinate system of the primary current is and the estimated current is{circumflex over ( )}; and
xcfx86rxcex1{circumflex over ( )} and xcfx86rxcex2{circumflex over ( )} indicate the orthogonal 2-axis component in the static coordinate system of the estimated flux xcfx86r{circumflex over ( )}.
The estimated speed xcfx89r{circumflex over ( )} thus obtained as described above is used in an arithmetic operation of the deviation between the speed and the speed target value xcfx89r* not shown in FIG. 1, the deviation is input to a speed adjustment unit, and a torque current command 113 is generated.
In the above mentioned conventional speed estimating method, when the voltage applied to the motor and the frequency of the current are considerably low (frequency of 0 in an extreme example), the induction reactance of the motor logically approaches zero, and the voltage of the inductance approaches zero regardless of the current. Therefore, the secondary flux cannot be computed from the primary voltage, and the estimated flux or the estimated speed cannot be computed, either. That is, the deviation between an estimated flux and its actual value, and the deviation between an estimated speed and its are not equal to zero, and do not successfully converge.
Generally speaking, since it is difficult to stably estimate the speed in an area in .which the frequency of the voltage applied to a motor is extremely low, there has been the problem with the conventional technology that a motor cannot be operated by speed sensorless vector control. That is, since there is a lower limit for the output frequency of the sensorless vector control-apparatus using an inverter, there has been a request to extend the range of speed control in the above mentioned low speed area.
To solve the above mentioned problems, the present invention aims at providing the speed sensorless vector control apparatus capable of operating a motor without its any trouble by successfully performing a stable speed estimation even in a low speed area in which the frequency of a voltage applied to the motor is extremely low.
The speed sensorless vector control apparatus according to the present invention includes a current/flux operation unit, a coordinate conversion unit, a current adjustment unit, a coordinate conversion unit, an inverter for driving an AC motor, and a speed estimation unit.
According to the first aspect of the present invention, the current/flux operation unit computes the primary current estimated value (hereinafter referred to as an estimated current) and the secondary flux estimated value (hereinafter referred to as an estimated flux) from the primary current, the primary voltage, and the estimated speed of the AC motor without a speed sensor. The coordinate conversion unit converts the primary current into a torque current and a magnetization current with the estimated flux vector set as the reference of a rotation coordinate. The current adjustment unit adjusts the torque current and the magnetization current such that they match respective commands. The coordinate conversion unit generates the primary voltage command by converting the coordinates of the output signal of the current adjustment unit with the estimated flux vector set as the reference of a rotation coordinate. The inverter for driving an AC motor is operated at the primary voltage command. The speed estimation unit receives an estimated current, an estimated flux, a primary current, a torque current, a magnetization current, and a primary frequency command value, and adds a product of the magnetization current deviation between the actual value of the magnetization current and the estimated value, the size of a torque current correspondence value, the sign correspondence value of the primary frequency command value, and the gain to the outer product of the estimated current deviation between the primary current and the estimated current and the estimated flux, thereby computing the estimated value of the speed of the motor.